As urban development fragments plant distributions, many small populations are at higher risk for reduced pollinator services and inbreeding depression.  We investigated the impact of population size on reproductive success of Iris atropurpurea (Dinsmore), a rare and endemic species of the central Israeli Mediterranean coast.  In seven large and seven small populations of Iris, we compared fruit set, seeds per fruit, and seeds per flower between hand-pollinated and open-pollinated flowers. 

Results/Conclusions

Our results indicate that in both large and small populations, irises were pollinator-limited, and that seeds per fruit in hand-pollinated flowers from small populations was significantly lower than in hand-pollinated flowers from large populations.  Moreover, in small populations, we found higher seeds per fruit in flowers hand-pollinated with pollen from other populations than in flowers hand-pollinated with pollen from within the same population, although this difference was not significant due to low sample size.  These results suggest that 1) pollinator services are limiting Iris reproductive success and that 2) small populations are potentially showing signs of inbreeding depression due to mate limitation.  Therefore, within the numerous small populations of Iris, individuals may be compromised in their ability to reproduce sexually, and may be unable to adapt sufficiently to environmental change.